This is irrelevant. Jane believes depictions of violence among teenagers in particular influence young people, so the most violent characters being adults doesn’t matter to her argument.

This strengthens Jane’s argument because it suggests that curbing violence between teenagers on shows marketed towards young people will have an effect on their behavior.

This is irrelevant. Jane doesn’t claim prohibiting violent depictions will be easy, or even possible. Some people may resist such a ban, but that wouldn’t affect her conclusion, which is a value judgment.

This weakens Jane’s argument. It suggests violence shown in movies doesn’t cause much of the violence perpetrated by young people.

This doesn’t mean the ban Jane’s advocating already exists, in whole or in part. There’s no indication such producers make shows meant for young people or that they exclude violence among teenagers from those shows.